This invention relates in general to universal joint assemblies, such as are commonly used in drive train systems for vehicles. In particular, this invention relates to an improved structure for such a universal joint assembly that facilitates the precise co-axial alignment of the rotational center of a cross with the rotational center of an end fitting to minimize rotational imbalance.
Drive train systems are widely used for generating power from a source and for transferring such power from the source to a driven mechanism. Frequently, the source generates rotational power, and such rotational power is transferred from the source to a rotatably driven mechanism. For example, in most land vehicles in use today, an engine/transmission assembly generates rotational power, and such rotational power is transferred from an output shaft of the engine/transmission assembly through a driveshaft assembly to an input shaft of an axle assembly so as to rotatably drive the wheels of the vehicle. To accomplish this, a typical driveshaft assembly includes a hollow cylindrical driveshaft tube having a pair of end fittings, such as a pair of tube yokes, secured to the front and rear ends thereof. The front end fitting forms a portion of a front universal joint assembly that connects the output shaft of the engine/transmission assembly to the front end of the driveshaft tube. Similarly, the rear end fitting forms a portion of a rear universal joint assembly that connects the rear end of the driveshaft tube to the input shaft of the axle assembly. The front and rear universal joint assemblies provide a rotational driving connection from the output shaft of the engine/transmission assembly through the driveshaft tube to the input shaft of the axle assembly, while accommodating a limited amount of angular misalignment between the rotational axes of these three shafts.
Each of the universal joint assemblies typically includes a cross having a central body portion with four cylindrical trunnions extending outwardly therefrom. The trunnions are oriented in a single plane and extend at right angles relative to one another. A hollow cylindrical bearing cup is mounted on the end of each of the trunnions. Needle bearings or other friction-reducing structures are provided between the outer cylindrical surfaces of the trunnions and the inner cylindrical surfaces of the bearing cups to permit rotational movement of the bearing cups relative to the trunnions during operation of the universal joint. In the front universal joint assembly of the above-described driveshaft assembly, the bearing cups supported on the first opposed pair of the trunnions on a front cross are connected to the front end fitting of the driveshaft assembly, while the bearing cups supported on the second opposed pair of the trunnions on the front cross are connected to an end fitting secured to the output shaft of the engine/transmission assembly. Similarly, in the rear universal joint assembly of the above-described driveshaft assembly, the bearing cups supported on the first opposed pair of the trunnions on a rear cross are connected to the rear end fitting of the driveshaft assembly, while the bearing cups supported on the second opposed pair of the trunnions on the rear cross are connected to an end fitting secured to the input shaft of the axle assembly.
In order for the driveshaft assembly to be properly balanced for rotation during use, it is important that the rotational center of the cross of the universal joint assembly be co-axially aligned with the rotational center of the end fitting to which it is connected (and, therefore, with the remainder of the driveshaft assembly) when there is no angular misalignment therebetween. Such co-axial alignment minimizes the overall amount of imbalance in the driveshaft assembly that may need to be corrected to prevent the generation of undesirable noise or vibration when the driveshaft assembly is rotated during use. In the past, the rotational center of the cross has been retained in co-axial alignment with the rotational center of the end fitting by mechanical retainers that were secured to the end fitting and abutted the bearing cups supported on the cross. A variety of such mechanical retainers are known in the art. In one known structure, the mechanical retainers are embodied as snap rings that are disposed in grooves machined in the inner surfaces of a pair of aligned openings formed through respective arms of the end fitting. The snap rings engage end surfaces provided on the bearing cups to retain them and the cross in position relative to the end fitting. In another known structure, the mechanical retainers are embodied as clips that are secured to the opposed outer surfaces of the arms of the end fittings. The spring clips also engage the end surfaces of the bearing cups to retain them and the cross in position relative to the end fitting.
Although these known mechanical retainers have been effective, it has been found that the stack-up of manufacturing tolerances of the various components can result in imprecise positioning of the rotational centers of the cross and the end fitting. As a result, it has been found that the overall amount of imbalance in the driveshaft assembly that may need to be corrected to prevent the generation of undesirable noise or vibration when the driveshaft assembly is rotated during use can be undesirable large. Accordingly, it would be desirable to provide an improved structure for a universal joint assembly that facilitates the precise co-axial alignment of the rotational centers of the cross and the end fitting.